Enhanced Photoluminescence, Mesomorphism and Conformation of Liquid-Crystalline Conjugated Polymers with Terphenyl Mesogen Pendants

A variety of LCCPs containing terphenyl pendants based on polyacetylene, polythiophene, poly(p-phenylene) and a poly(p-phenylene) copolymer backbone have been synthesized. The effects of the structural variation on their properties, especially their mesomorphism, photoluminescence and secondary structures, were studied systematically. Longer alkoxy spacer favor stronger light emission and better mesomorphism. Disubstituted polyacetylenes show better developed mesomorphic textures, higher quantum yields and better thermal stability than their corresponding monosubstituted analogs. Steric effects and the "jacket-effect'' from the mesogens cause the bulky terphenyl mesogen pendants to rotate around the main chain and force the main chain to assume a spiral conformation along the main chain in long range.